Fluorescent reporter molecules are used for microscopy, real-time PCR, microarrays, and other applications. Yet most fluorescent dyes share some fundamental flaws: They are subject to photobleaching, are not very bright, and have overlapping emission and absorption spectra. Some nanotechnologists are betting that quantum dots (QDs) will eliminate these problems.
QDs consist of a nanometer-scale crystalline core of semiconductor material; biologically active versions are surrounded by a protective shell and external coat. Unlike fluorophores, which have distinct absorption spectra, QDs absorb light over a wide spectral range; researchers can use lasers, arc lamps, or LEDs as light sources. But each QD emits light over a narrow spectrum, the exact color depending on the particle's diameter and composition. Thus, a collection of different QDs can be used to multiplex applications using only a single excitation source. QDs are also relatively photostable, even during intense excitation, and are brighter than fluorophores.
Last November, ...
